Not only does Pius XI answer in the negative, Mortalium animos makes it crystal clear that men who merely support those who arrange such meetings are doing something that he deems "tantamount (i.e., equivalent in value, significance, or effect) to abandoning the religion revealed by God." Well, like it or lump it, that IS the definition of apostasy.
Imagine what he would have said about Assisi and those responsible! He would not have said, "Oh, well it was not THAT bad...JP2 didn't actively participate in the worship the Great Thumb in union with Mr. John Pretty-on-Top, so it was, at worst, just scandalous..."
The Great Thumb, people! As with the Obamanator, we must ask: WTH would these men have to do to make it register that they are NOT what they pretend to be?